The present invention relates generally to fiber optic silicon microbench devices and optical switches. More particularly, it relates to an apparatus having refractive and/or reflective components for equalizing optical pathlengths in a fiber optic switch.
Fiber optic devices are commonly used for optical communications and optical computer. networking. Optical data networks often have crossbar switches for switching optical connections between different fibers in two coupled fiber arrays.
FIG. 1 shows a typical silicon microbench crossbar switch 24 according to the prior art. Input optical fibers A-C 20 are coupled through GRIN lenses 22 to the switch 24. The switch 24 has pivotable micromechanical mirrors 26, 28 that can be in a horizontal position or a vertical position. Output fibers D-F 30 are coupled to GRIN lenses 32 and are aligned to receive light from vertical mirrors 26. Mirrors 26 are in a vertical position; mirrors 28 are in a horizontal position.
Mirrors 26 in the vertical position reflect light to the output fibers 30, Mirrors 28 in the horizontal position do not reflect light. Any input fiber A-C 20 can be coupled to any output fiber D-F 30 with appropriate control of the mirrors. One problem with the device of FIG. 1 is that different mirror configurations provide different optical path lengths between the input fibers and output fibers. For example, the connection between fibers B and D is shorter than the connection between fibers C and E. Therefore, as the switch connections change, the optical paths lengths change and the beam spreading characteristics change. This renders it impossible to optimize the focusing characteristics of the GRIN lenses for all possible connections. Another undesirable result is that the optical loss of the switch is different for different connections.
U.S. Pat. No. 5,841,917 discloses a crossbar switch that has input and output optical fibers arranged in a staggered fashion. The staggered fibers equalize the optical path lengths for all possible connections. A problem with this approach is it precludes the use of conventional, nonstaggered V-groove fiber arrays and monolithic microlens arrays. Staggered fiber arrays terminated with individual GRIN lenses tend to be more expensive and difficult to assemble than conventional V-groove fiber arrays that are coupled to monolithic microlens arrays.
There is a need for a fiber optic crossbar switch that has equalized effective optical path lengths for all connections, and is compatible with conventional, nonstaggered fiber array components.
Accordingly, it is a primary object of the present invention to provide a fiber optic crossbar switch that:
1) provides equalized beam spreading characteristics for all possible connections;
2) does not require that the optical fibers and lenses be arranged in a staggered fashion;
3) is compatible with conventional nonstaggered fiber arrays such a V-groove arrays and with monolithic microlens arrays.
These and other object""s and advantages will be apparent upon reading the following description and accompanying drawings.
These objects and advantages are attained by the present apparatus for switching optical signals. The apparatus has an optical switch that utilizes reflective elements arranged such that different switching configurations create different optical paths between the input and output fibers. For example, the apparatus can have a crossbar switch with reflective elements arranged in at least two columns and two rows. There are at least two waveguides (e.g. optical fibers) directed toward the reflective elements. Finally, the apparatus has an input stairstep block disposed between the waveguides and the crossbar switch. Each waveguide is associated with a different optical path through the switch. The stairstep block is oriented so that the longest optical path through the stairstep block is associated with the longest optical path through the switch.
Preferably, the steps of the stairstep block have. a length that is accurately sized in accordance with the spacing between reflective elements in the switch. The present invention provides equations for relating these distances and the refractive index of the stairstep block.
Preferably, the apparatus includes at least two output waveguides for receiving light transmitted by the input waveguides and reflected by the reflecting elements.
Also preferably, an output stairstep block is disposed between the output waveguides and the switch.
The stairstep blocks can have a rectangular shape, or a slanted shape.
The stairstep blocks can have beveled or anti-reflection coated endfaces to reduce backreflection into the optical waveguides.
Also, the stairstep blocks can have one less step than the number of waveguides. For example, if there are K input waveguides, then the input stairstep block can have K-1 steps.
The present invention includes embodiments having a prism instead of a stairstep block disposed between the waveguides and the switch.
The present invention also includes embodiments having a small prism or a small reflector associated with each waveguide, wherein the arrangement of the fiber arrays and prisms or reflectors provides equalized beam paths for all possible switching connections.